Speed class
A characteristic that describes the minimum write speed to the card. It is given for SD and microSD cards (including their variations, see "Type") and is indicated by a number indicating the speed in MB / s: for example, class 10 corresponds to 10 MB / s.
Higher speeds provide more options, but come at a higher cost; in addition, it must be supported by the equipment where the card is used. So the choice for this parameter depends on the capabilities of such equipment and specific tasks. High speed is of key importance for video recording: for example, for video in Full HD (1920x1080) you need a card with a class of at least 4, and preferably 6 or even 10 (such characteristics already allow you to work with an increased frame rate).
Note that in the characteristics of many memory cards, you can see seemingly inconsistent figures. For example, a class 10 model can correspond to UHS Class 3 (which means the speed is no longer from 10, but from 30 MB / s) and the video recording class V60 (and this is already from 60 MB / s); and the overall write speed for it can be claimed at an even higher level — for example, 80 MB / s. All of these options are described in detail below; and here we note that there are no inconsistencies here. The fact is that the data regarding the UHS capabilities and the video recording class are relevant for operation via the UHS bus; if the card reader does not have such a bus, then the card's capabilities are limited by the...general speed class. So, the model from our example in a card reader without UHS will be able to issue a maximum of 10 MB / s; and if you have UHS, it will work at least 60 MB / s, which does not contradict the requirements of UHS Class 3 (at least 30 MB / s). The overall write speed is usually indicated by the theoretical maximum, and in fact its value is often noticeably lower.
UHS class
UHS bus version supported by the memory card.
UHS is a data exchange technology used in SD/microSD cards of the (micro)SD HC and (micro)SD XC standards. It allows you to significantly increase the speed of data exchange compared to previous standards; at the same time, media supporting this technology are quite compatible with equipment that does not have UHS - except that the speeds in such cases will be limited by the capabilities of the card reader, and not the card itself.
As for the versions, their names consist of two parts: UHS generation (I or II) and class (1 or 3) - for example,
UHS-I Class 1. Actually, this is the most modest version of UHS found in modern memory cards; in addition to it,
UHS-I Class 3 and
UHS-II Class 3 are popular. The maximum data transfer speed (usually referring to read mode) depends on the UHS generation - it is 104 MB/s for version I and 312 MB/s for version 2. “Class”, in turn, determines the lowest (guaranteed) write speed : it is at least 10 MB/s for Class 1 and at least 30 MB/s for Class 3. Different versions of UHS are quite compatible with each other, except that the speed in such cases will be limited by the slower standard.
Note that for UHS cards, more advanced characteristics may be indicated in other paragraphs - for example, the video recording class (see below) V90 for a UHS-II Class 3 card. There
...is no contradiction here: the speed of 90 MB/s provided by such a card in recording mode, it fully satisfies the “not lower than 30 MB/s” condition provided for UHS Class 3.Video recording class
The video recording class supported by the memory card.
This parameter is indicated for SD/microSD cards and their variations, as well as CompactFlash (see “Type”). In the first case, the format designation V* is used, in the second - VPG*, but the idea is the same in both cases: the numbers indicated instead of an asterisk are the lowest write speed (in MB/s) that the card is guaranteed to provide. This speed is of key importance primarily in video recording, which is why this parameter is called “Video Recording Class”; the higher it is, the higher the resolution and frame rate at which you can record using this card.
The minimum video recording class found in modern SD/microSD family cards is
V6, which already allows you to work with HD and Full HD video. However, for Full HD it is advisable to have a card of at least
V10 level. And the
V30 class already allows you to comfortably work with Ultra HD 4K. Faster cards are also being released - V60 and even V90, suitable for resolutions of 8K and higher.
In turn, in CompactFlash cards you can find models of the
VPG20,
VPG65 and
VPG130 classes
Note that the video recording class may well be higher than the general speed class and/or UHS class (see above). However, there are no contradic
...tions here. UHS class requirements require write speeds of “not less than...”; Thus, for example, all cards with a video recording class of V30 and higher will comply with the UHS Class 3 standard (“not lower than 30 MB/s”). And the general speed class describes the capabilities of the card when working with equipment without UHS support (and such equipment is practically not used in video recording).Speed value
The coefficient describing the maximum speed of the card in read mode. In this case, 150 KB/s is taken as a unit; thus, for example, the speed value of 533x corresponds to 150*533=79,950 KB/s, i.e. about 80 MB/s.
In general, this parameter is quite specific; in practice, it is easier to focus on the directly declared reading speed (see below). However, sometimes it is not specified - in such cases, the speed value will be most useful.
Read speed
The maximum speed of reading data from a memory card.
Any modern memory card provides sufficient reading speed for simple everyday tasks — like copying photos from a camera to a laptop. Therefore, it makes sense to pay attention to this parameter mainly in cases where the card is purchased for professional use, or if high speed is critical for you — for example, if you often have to copy photos from the camera in a hurry. In doing so, two points should be taken into account. Firstly, the corresponding speed must be supported by the card reader where the card is used. Secondly, this paragraph indicates the theoretical maximum — in perfect conditions; the actual reading speed may be lower (if we are talking about cards with UHS, this speed can be estimated by the UHS class, see above about it). Nevertheless, it is quite possible to compare different models of cards by this indicator: differences in theoretical speed usually quite correspond to the difference in actual speed.
Write speed
The maximum speed for writing data to a memory card.
High write speed is important for tasks that involve storing large amounts of data in a limited amount of time. However, note that this paragraph indicates the theoretical maximum speed for perfect conditions; in fact, this value can be noticeably lower. Therefore, the characteristics of memory cards also indicate the minimum guaranteed write speeds in different modes — the general speed class, the UHS class, the video recording class and/or the class for applications. All of them are described in more detail above. However, you can also evaluate the capabilities of the carrier by the overall speed: other things being equal, a card with a higher theoretical speed will work faster in fact.
As for specific values, speeds
from 4 MB / s and
from 6 MB / s are practically not found nowadays,
from 10 MB / s and from
16 MB / s can be called average indicators,
from 50 MB / s — above average, and the fastest models have a maximum write speed of
100 Mbps or more.
